Technological advances should make breast and cervical screening more accurate in future, say experts.

Both have already been partly credited with reducing death rates from these cancers, although some critics question whether the benefits to women outweigh the risks.

At worst, they say, screening can mean that women undergo operations or treatments they do not need, because screening has made a mistake and identified a tumour that is not there.

The latest techniques could boost the accuracy rates and dismiss these criticisms once and for all.

In 1986, there were only 100 mammography units in the whole of the UK, but the following few years saw a revolution which extended screening to millions more.

Changes arriving in radiography - many driven by a revolution in computer technology - could improve it yet further.

Film trouble

Breast scans are currently stored on photographic films, but in future they are likely to be kept as computer images instead.

Computer technology could help screeners

Dr Rosalind Given-Wilson, a consultant radiologist at St George's Hospital and clinical director of the South West London Breast Screening Service, said that this would eliminate many of the problems linked to scans.

She said: "If the image comes out too dark or too light, you have to do it all again.

"If it is on computer, you can correct the exposure."

Not only does computerisation improve the quality of the images, it also potentially gives radiologists a vast archive of scans for comparison at the touch of a button.

The eDiamond scheme involves a "virtual database" of hundreds of thousands of breast scans from dozens of hospitals.

Computer checks

Many experts believe it is only a matter of time before some responsibility for the assessment of scans falls to the machines as well.

The first results coming through, however, are showing some increases in cancer detection

Dr Rosalind Given-Wilson

Computers are already being asked to mark with a cross on the scan any areas they think may be cancerous.

Dr Given-Wilson said: "The problem is that the computer can be fooled by a lot of simple things even such as a skin fold.

"The first results coming through, however, are showing some increases in cancer detection."

Computers may also play a role in the examination of cervical screening tests.

The way these are carried out has not changed much for decades.

In a scrape

A wooden spatula is used to take a scraping of cells from the cervix, and these are deposited onto a microscope slide and sent off to a laboratory.

There are a number of reasons why this can be less than ideal, says Dr Nick Longsdale, a consultant histopathologist from the Norfolk and Norwich Hospital.

Liquid-based cytology could replace slides

He said: "Approximately one in 10 slides has to be repeated because it is of inadequate quality.

"This could mean there are not enough cells on the slide to form a judgement,or that the cells are overlapping or obscured by blood or other inflammatory cells."

In addition, because the sweep of the spatula is taken from just one part of the cervix, a cancer or pre-cancer growing elsewhere on the neck of the womb may be missed completely.

One possible answer to this is "liquid-based cytology", under test at various pilot sites around the UK.

Instead of the spatula, a brush is used to gather cells from various parts of the cervix, instead of one area.

This is then placed into a vial of fixing fluid, and swished around to loosen the cells and transfer them into the fluid.

The liquid is then sent off to the lab.

Better view

A machine at the lab centrifuges the cells and filters them - producing a slide which has an even representation of all the different cells in the fluid spread over a tiny area in the centre of the glass.

The screener can then check just this blob of fluid - much quicker - and in theory much clearer and easier to interpret.

Dr Longsdale said: "The staff have found it much easier to use - and far fewer slides have to be rejected as inadequate."

Computer-assisted screening could work here too - again highlighting suspect "areas" of cells to be re-checked by the screeners.

But it is likely to be some time before the NHS trusts a machine to do all the checking.